This invention relates to rubber derivatives, More particularly, the invention provides hydrophilic rubber derivatives that are wholly or partially soluble in water or will form very stable aqueous emulsions or colloidal solutions.
Many different natural and synthetic rubber derivatives are known.
For example, rubbers containing double bonds have been epoxidised to provide derivatives with active sites that can be utilized to introduce various other molecules to provide rubbers with desired modified properties.
Numerous attempts have been made to produce water-soluble rubber derivatives, which would be useful for a wide variety of purposes but to date all that has been achieved is derivatives that can be used to form aqueous suspensions of limited stability and from which the derivative settles out after a short period.
According to the invention, a rubber derivative comprises a coordination compound of a natural or synthetic rubber containing double bonds and/or epoxy or other groups containing an electronegative atom or atoms and preferably having a weight average molecular weight of from 20,000 to 90,000, more preferably, 20,000 to 85,000, especially about 80,000, with an alkali or alkaline earth metal.
Typical of the rubbers that can be used to form the coordination compound derivatives of the invention are natural rubber (cis-polyisoprene), preferably liquid natural rubber, trans-polyisoprene, neoprene, nitrile rubber, polybutadienes and epoxidised rubbers, especially liquid epoxidised polyisoprenes or blends of such rubbers.
Although the coordination compounds of the invention are preferably formed using rubbers of relatively low average molecular weight, the compounds will also form in the presence of larger rubber molecules so it is possible to form the coordination compounds from the lower molecular weight component of any rubber but at lower yield.
The metal component of the coordination compound is preferably an alkali metal, more preferably potassium or sodium, but alkaline earth metals, preferably calcium, can also be used to form coordination compounds. Mixtures of metals, for example of potassium and sodium or lithium or potassium and calcium can also be used.
Since, in order that strong intra-coordinated bonds are formed, the rubber molecules must wrap round the metal atoms so that bonds can form at a plurality of sites, the size of the metal atoms must be taken into consideration. If they are too small the rubber molecules may not be sufficiently flexible to wrap closely around the metal atom so that the active sites on the rubber molecules will be too far from the metal atoms for a number of bonds to form and if they are too big the metal atoms may not be able to enter the spaces available in the rubber molecules However it is believed that both intra- and inter-coordinated bonds are formed and that inter coordinated bonds may be formed between the rubber and larger or smaller metal atoms.
The rubber derivatives of the invention are hydrophilic and can be dissolved in water to form clear, brownish solutions. Where the derivatives are made from rubbers with higher molecular weight components, any coordination compounds formed from such components may not be wholly water soluble but the derivatives will still form suspensions of the insoluble portion in a solution of the soluble portion that remain stable for a number of years.
The derivatives of the invention may be made by dissolving a rubber containing double bonds and/or epoxy or other groups containing an electronegative atom or atoms and having at least a component with a weight average molecular weight in the range of from 20,000 to 90,000, more preferably, 20,000 to 85,000, especially about 80,000, in a polar solvent, adding to the solution an at least equivalent amount of powdered alkali metal and/or alkaline earth metal hydroxide and/or carbonate, optionally together with a desiccant, if the solvent is not water-free, stirring the mixture until a coordination compound between the rubber and the metal atoms has formed and separating the coordination compound from the solvent.
The polar solvent is preferably 1,4-dioxane or tetrahydrofuran.
The mixture of rubber solution and metal is preferably heated under reflux with continuous stirring, preferably for a period of from three to twenty four hours. The solution is preferably evaporated to dryness and then the residue is further dried under vacuum.
When a rubber having a high average molecular weight is to be used in the preparation of the derivatives, prior to addition of the base, the rubber is preferably heated under reflux in a polar solvent for sufficient time to break at least some of the molecular chains to reduce the molecular weight, whereby the yield of derivative will be increased.
The residue can then be taken up in water and, provided that the pH of the solution or suspension remains above 7, the solution or suspension is stable indefinitely. However, when the solution or suspension is acidified, for example by the addition of dilute hydrochloric or other acid, the coordinated bonds break and the rubber is precipitated.
This surprising phenomenon gives rise to some very special uses of the rubber derivatives of the invention in that they can be used very effectively as water treatment agents.
If even a small amount of a dilute solution or suspension is added to water containing suspended or dispersed pollutants and then acid is added the precipitated rubber gathers up the pollutant and forms an easily separable matrix containing the pollutant. If the density of the pollutant is lower than that of water the precipated rubber carries the pollutant with it to the surface of the water where it can be readily separated from the water, for example, by skimming.
Thus, the derivatives can be used for cleaning water containing very fine, unfilterable particulate material, such as smoke residue, carbon or wood dust, or finely dispersed liquid material, such as oil droplets, in a very simple and cost effective manner.
The derivatives can be used alone or together with conventional flocculants or coagulants, for example, salts or oligomeric or polymeric materials, such as chitin or chitosan and various acrylic polymers.
Moreover, the derivatives can be used to extract or remove ions, particularly metal ions, such as, for example, copper, nickel, iron, tin, platinum, gold, chromium, mercury and lead, from water or to clear water from pungent odours or undesired pigmentation. The derivatives can be used either as the sole treatment agent or in conjunction with another ion removing material, by adding to the water the ion removing material for example activated charcoal or an ion exchange resin or a zeolite or chitin or chitosan, to trap the ions and then adding the derivative and acidifying. Minute particles of the ion removing material that would otherwise be difficult to remove after a conventional treatment can therefore be easily removed. In this application, the derivatives may be used to reclaim useful metals from water.
The derivatives can also be used to produce water-based rubberized adhesives, paints and coatings, which has never previously been possible.
They may also be used as a slow-release binding matrix for fertilisers and pesticides. To produce such products, the active principle is dissolved or suspended in water, the derivative solution is added followed by acid and the rubber matrix containing the active principle which forms is collected. Fertilisers and pesticides in this form have the advantage that they are not washed away so readily in a heavy downpour.